Kinetics of a Reaction of 3-Chloroacetylacetone with Thioureas

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Kinetics of a Reaction of 3-Chloroacetylacetone with Thioureas a B.. Zaware*, b R. A. Mane and c. R. Kuchekar a New Arts Commerce and cience College, Ahmednagar (M.

1 Kinetics of a Reaction of 3-Chloroacetylacetone with Thioureas a B.. Zaware*, b R. A. Mane and c. R. Kuchekar a New Arts Commerce and cience College, Ahmednagar (M..), India b Department of chemistry, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad c Post Graduate Department of chemistry, P.V.P. College Pravaranagar, Loni Abstract The kinetic study of 3-chloroacetylacetone and s has been carried out in ethanol. Thioureas used for study are, phenyl, p-methyl phenyl, p-ethoxy phenyl and p-chlorophenyl. The second order rate constants for these reaction were reported. The rate of reaction is first order with respect to 3-chloroacetylacetone and first order with respect to s. The effect of substituents on the rate of reaction was also studied. Thermodynamic parameters are used to explain the nature of the reaction. The reaction products are isolated and characterized. Possible reaction mechanism for the reaction will be proposed and details of the kinetics will be discussed. Key words: Kinetics, Reaction, 3-Chloroacetylacetone, Thiourea. Introduction Thioureas are commercially used in photographic films, plastics and textiles. Thioureas have shown antibacterial, fungicidal[1], hypnotic and antipyretic[2] activities. ome of the s are screened for anticancer activity[3-5]. The use of thiozoles as a vulcanizing accelerators and dye intermediates has been reported[6]. Kinetic and thermodynamic studies on reactions of Pt(II) complexes with pyrozole and 1,2,3 triazole has been carried out[7]. Reaction kinetics of gold dissolution in acid solution using ferric sulphate as a oxidant was investigated with rotating disk technique[8]. Kinetics and mechanism of reactions between and iodate in buffer medium has been studied[9]. The kinetics of the reaction of with formaldehyde was studied[10]. Kinetics of oxidation of s by using various oxidizing agents has been studied[11]. The kinetic study of reactions of thioamides[12] with phenyl bromides is also studied. Kinetics of condensation of allyl/alkyl bromides and allyl s / thioamides[13] has been reported. We Available online at 276

2 have reported kinetic study of reaction of chloroacetone with s[14]. Literature survey reveals that there is no work on kinetic study of reaction of 3-chloroacetylacetone with s. Experimental ection 3-chloroacetylacetone (Fluka), sodium hydroxide, diethyl ether and phenolphthalein (Qualigens) were used. Aryl s were prepared by Frank and mith method[15]. Double distilled absolute alcohol was used as solvent to prepare standard solutions of 3-chloroacetylacetone and s. Glass distilled water was used throughout the study. Kinetic measurements were carried out at different concentrations of reactants and temperatures. A solution containing appropriate amount of which is thermostated at particular temperature was added in solution containing appropriate amount of 3-chloroacetylacetone at the same temperature. At different time intervals definite volume of aliquot was added to a mixture of diethyl ether and distilled water. It was shaken immediately and the aqueous layer containing thiozole hydrochloride was titrated[16] against standard sodium hydroxide solution using phenolphthalein as an indicator. Under similar experimental conditions equal amount of and 3-chloroacetylacetone were mixed and kept overnight. Then reaction mixture was poured on crushed ice. Unreacted reactants were removed by ether extraction. The white solid was crystallized in ethanol and characterized as 2-(substituted amino) 4 methyl 5-acetyl thiozoles on the basis of the reported melting points and their spectral data. Results and Discussion The stoichiometric study indicates the one mole of reacts with one mole of 3- chloroacetylacetone. The rates of reaction were measured at different concentration of at constant concentration of 3-chloroacetylacetone. The plot of log (dc / dt) against log [ ] was straight line and slope of the plot is nearly one. imilarly the rates were determined at different concentration of 3-chloroacetylacetone by keeping concentration of s constant. The plot of log (dc / dt) against log [3-chloroacetylacetone ] is also straight line and slope of the plot is nearly one. By using Van t off s differential method[17] the order of reaction with respect to 3-chloroacetylacetone and s was also determined. econd order rate constants were determined at five different temperatures. The energy of activation (Ea) was determined by plotting graph of log k verses 1/T and other thermodynamic parameter were calculated, [Table-1] The entropies of activation ( * ) of these reaction are negative indicates rigid nature of the transition state. The negative value of entropies of activation ( *) also indicates that less stable noncyclic reactant convert into stable cyclic products. Almost equal values of free energy of activation ( F* ) for all s indicates that probably a similar type of mechanism prevails in all cases. When rate constants for the reaction are compared, the is found to be more reactive than the substituted phenyl s. This may be due to the presence of Л-electron in benzene ring. The phenyl and p-methyl phenyl show nearly same rate constants. This may be due to small effect of methyl group due to hyper conjugation and inductive effect. The p-ethoxy phenyl shows higher rate of reaction due to mesomeric effect. Available online at 277

3 Table 1: Thermodynamic parameters for reaction of 3-chloroacetylacetone with s Thioureas Ea* kj mol -1 * kj mol -1 - * Jk -1 mol -1 F* kj mole -1 Thiourea Phenyl p-methyl phenyl p-ethoxy phenyl p-chlorophenyl The p-chlorophenyl shows lower rate of reaction due to negative inductive effect of chloro group. In all the reactions 3-chloroacetylacetone is more reactive than chloroacetone[13] as the presence of electron withdrawing group stabilizes enol intermediate in the formation of thiozole. It is found that, the reaction is second order, first order with respect to and first order with respect to 3-chloroacetylacetone. The rate constants calculated from second order rate law are fairly constant [Table 2]. Table 2: econd order rate constants for reaction of 3-chloroacetylacetone with s. Thiourea = 0.05 mol dm 3 Temp = K Thioureas 10 3 dm 3 mol -1 s -1 at 3-chloroacetylacetone mol dm Thiourea Phenyl p-totyl p-phenitidinyl p-chlorophenyl Based on these facts, the following general mechanism and rate expression is proposed. k 1 low Fast [ Intermediate ] products ---- ( 1 ) k 1 k 2 1 stands for 3-chloroacetylacetone and 2 stands for s. Rate of reaction = k 1 [ 1 ] [ 2 ] - k -1 [ Intermediate ] ( 2 ) Available online at 278

4 On applying steady state approximation. d / dt [ Intermediate ] = o = k 1 [ 1 ] [ 2 ] - k- 1 [ Intermediate ] - k 2 [ Intermediate] ( 3 ) k 1 [ 1 ] [ 2 ] [Intermediate] = ( 4 ) k 1 + k 1 3 C +δ +δ O-δ -δ C l -δ +δ C N 2 N low 3 C O - N + C + N C l - Fast 3 C O N C l N 3 C N C l N + 2 O Fast O C 3 N C l N 3 C O, ph enyl, p-m e thyl ph enyl, p-ethox y p hen yl, p -ch loroph enyl chem e I Available online at 279

5 ubstituting the value of [ Intermediate ] in equation ( 2 ) k -1 k 1 [ 1 ] [ 2 ] Rate of reaction = k 1 [ 1 ] [ 2 ] ( 5 ) k 1 + k 2 K -1 k 1 Rate of reaction = k- 1 - [ 1 ] [ 2 ] ( 6 ) K 1 + k 2 If k = k -1 - k -1 k 1 k 1 + k 2 Rate of reaction = K [ 1 ] [ 2 ] The order of reaction is two. The derived rate law explains all the observed experimental facts. Conclusion The rate of reaction between 3-chloroacetylacetone and is found to be two. The proposed rate law also shows that the rate of reaction is two. Nearly equal values of free energy ( F*) indicates that same type of reaction mechanism prevails. Decrease in entropy ( *) indicates that from open chain compound cyclic compounds are formed. Acknowledgement Authors are thankful to Prof. D. B. Ingle for his invaluable guidance. The authors (BZ) is thankful to authorities of A. J. M. V. Prsarak amaj, Ahmednagar (M..) for their kind help and BCUD, University of Pune for financial assistance and (RK) is thankful to PRE Pravaranagar. References 1. M Motani, J. Pharm. oc. Japan, 1952,72, K lotta ; etal, Chem. Ber., 1930,63B, W Aumulkar; Chem. Ber., 1952, 85, M Kajimoto, J. Pharm and Chem., 1952, 24, A chering, Chem. Abst., 1953, 47, G Pathrikar; Bondge; A Burungale; V Bhingolikar; R Ingle; R Mane, Indian J. Chem., 2002, 41A, J Rosic;B Petrovic; M Dojuran, Z. Bugarcic mono tshefre fur chemie, 2007,138, 1. Available online at 280

6 8. J Li;J Miller, ydrometallurgy, 2007,89 (3-4), Wang; J Lin; F. Chun; y x y Y an ; Q. Gao, cience in China B Chem.,2004,47 (6) K Dusek, J.Polymer ci., 2003, 30 (121) K Malhotra; A Garg; T. harma, J. Ind. Chem.. oc., 1987, 64, J Okamiya, Nippon Kgaku kaishi, 1965,86, T Rao; G Punraiah; E underah, J. Ind. Chem. oc., 1986, 63, B Zaware; R Mane; D Ingle, J. Ind. Chem. oc., 2000, 77, R Frank; P mith, Org. ynth., 1955, 3, Makhija; K Baparai, Analyst, 1981,106, J. Van t off Etude de Dynamique chemique Multer and compony, Amsterdam Available online at 281

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Pelagia Research Library Available online at www.pelagiaresearchlibrary.com Der Chemica Sinica, 2013, 4(1):100-104 ISSN: 0976-8505 CODEN (USA) CSHIA5 Oxidation of S-phenylmercaptoacetic acid by quinoxalinium dichromate K. G. Sekar*